While providing year-round colour and robust foliage in a garden, evergreens can also help block out noise. When planted in a row, they act as natural noise cancelers. The trick to using them in your garden is finding the appropriate type of tree and planting it carefully to muffle those noises you'd rather not hear, from honking cars to partying neighbours.
How It Works
Tree branches and leaves act as a barrier against noises -- and because evergreens maintain thick foliage year-round, they excel as sound barriers. The denser their foliage, the more effectively they block out sound. The key is making sure you string them in front of the source of noise, with extra evergreens on the edges so no noise rushes around the sides of the barrier.
Which Trees to Use
Some types of evergreen trees are more effective at cancelling noise than others. Horticulturalists recommend evergreens with dense foliage for soundproofing a garden on the Virginia Cooperative Extension website. Being thick, you need not plant many of these trees -- such as the Norway spruce or the Arborvitae -- to create a long row of trees. On the other hand, columnar junipers remain narrow as they grow upwards, making them ideal for a tight space; you also don't have to worry about stray branches growing over neighbours' fences.
To create an effective sound barrier, plant evergreen trees in a row or stagger them in close-woven groups for a more natural look. The Danish Road Institute recommends planting them close to the noise source or close to the house for optimal effect; planting them at the midpoint will let noise seep over the trees to the garden or home. At planting time, space thick evergreens 5 to 10 feet apart to accommodate their future spread, though you can always trim them if they grow too wide.
When planting your noise-cancelling trees, remember that most evergreens grow 40 feet tall or more over the course of their life. Give them plenty of space to grow to their full height, and be prepared to trim them when they hang into neighbours' yards. If you need a noise barrier right away, you can always opt for a fast-growing evergreen, such as the Leyland cypress or Japanese cryptomeria.